h264: fix bit depth changes with frame threading

AVCodecContext.bits_per_raw_sample is updated from the previous thread
in the generic update function before the codec specific update_thread
function is called. The check for reinitialization of dsp functions uses
bits_per_raw_sample. When called from update_thread_context it will be
already at the current value and the dsp functions aren't updated if
only the bit depth changes.

libavcodec/h264.c

@@ -1573,6 +1573,11 @@ static int decode_update_thread_context(AVCodecContext *dst,
          h->sps.chroma_format_idc != h1->sps.chroma_format_idc ||
          h->sps.colorspace        != h1->sps.colorspace)) {
 
+        /* set bits_per_raw_sample to the previous value. the check for changed
+         * bit depth in h264_set_parameter_from_sps() uses it and sets it to
+         * the current value */
+        h->avctx->bits_per_raw_sample = h->sps.bit_depth_luma;
+
         av_freep(&h->bipred_scratchpad);
 
         h->width     = h1->width;